WO2019026404A1

WO2019026404A1 - Cellulose nanofiber carbon and method for manufacturing same

Info

Publication number: WO2019026404A1
Application number: PCT/JP2018/020799
Authority: WO
Inventors: 正也野原; 周平阪本; 三佳誉岩田; 政彦林; 武志小松
Original assignee: 日本電信電話株式会社
Priority date: 2017-08-04
Filing date: 2018-05-30
Publication date: 2019-02-07
Also published as: CN110997563A; CN110997563B; EP3663259A1; US11319209B2; US20210163293A1; EP3663259A4; JP6936439B2; JPWO2019026404A1

Abstract

Provided is a cellulose nanofiber carbon for which the specific surface area can be increased and a method for manufacturing the same. This method for manufacturing a cellulose nanofiber carbon thermally treats a cellulose nanofiber to carbonize the same and involves: a freezing step S2 of freezing a solution or gel that includes the cellulose nanofiber to obtain a frozen body; a drying step S3 of drying the frozen body in a vacuum to obtain a dried body; and a carbonizing step S4 of heating and carbonizing the dried body in an atmosphere that does not cause the dried body to combust in order to obtain the cellulose nanofiber carbon.

Description

Cellulose nanofiber carbon and method for producing the same

The present invention relates to cellulose nanofiber carbon and a method for producing the same.

The carbon nanofibers generally have an outer diameter of 5 to 100 nm and a fiber length of 10 times or more of the outer diameter. Due to its unique shape, it has features such as high conductivity and high specific surface area.

Conventionally, as a method for producing carbon nanofibers, for example, an electrode discharge method, a vapor phase growth method, a laser method and the like are known (Non-Patent Documents 1 and 2). Further, methods of producing cellulose nanofibers by heat-treating cellulose that is derived from natural products are disclosed, for example, in Patent Documents 1 and 2.

Patent 5510092 Patent No. 5386866 gazette

The carbon nanofibers produced by the conventional production method have a problem that they are not elastic and plastically deformed so that they can not return to their original shape upon compression or bending, and the mechanical strength is low.

In addition, when heat treatment of cellulose nanofibers is attempted to obtain a carbon material, the cellulose nanofibers aggregate during drying, are sintered during heat treatment, become carbon materials with high density, and have a large specific surface area. There is a problem that is difficult.

The present invention has been made in view of this problem, and an object of the present invention is to provide cellulose nanofiber carbon having stretchability, high mechanical strength, and a large specific surface area, and a method for producing the same. .

The method for producing cellulose nanofiber carbon according to one aspect of the present invention is a method for producing cellulose nanofiber carbon for carbonizing cellulose nanofibers, which comprises freezing a solution or gel containing the cellulose nanofibers to obtain a frozen body. The gist of the present invention comprises a freezing step to obtain, a drying step of drying the frozen body in a vacuum to obtain a dried body, and a carbonizing step of heating and carbonizing the dried body in an atmosphere where the dried body is not burned.

In addition, the cellulose nanofiber carbon according to one aspect of the present invention has a gist that it has a three-dimensional network structure of a co-continuum in which cellulose nanofibers are connected.

Moreover, the cellulose nanofiber carbon which concerns on 1 aspect of this invention has a three-dimensional network structure which is a continuum which the nanofiber of bacterial production cellulose was connected.

According to the present invention, it is possible to provide a cellulose nanofiber carbon having stretchability, high mechanical strength and capable of increasing the specific surface area, and a method for producing the same.

It is a flowchart which shows the manufacturing method of the cellulose nanofiber carbon which concerns on 1st Embodiment of this invention. It is a SEM image of the cellulose nanofiber carbon produced by the manufacturing method of a 1st embodiment. It is a SEM image of the carbon material produced by the manufacturing method different from a 1st embodiment. It is a flowchart which shows the manufacturing method of the cellulose nanofiber carbon which concerns on 2nd Embodiment of this invention. It is a SEM image of the skin part of the carbon material obtained by example 1 of an experiment. It is a SEM image of the section of the carbon material obtained by example 1 of an experiment. It is a SEM image of the carbon material obtained by example 2 of an experiment. It is a SEM image of the carbon material obtained by comparative example 1. It is a SEM image of the carbon material obtained by comparative example 2. It is a flowchart which shows the manufacturing method of the bacteria-produced cellulose carbon which concerns on 3rd Embodiment of this invention. It is a SEM image of bacterial production cellulose carbon produced by the manufacturing method of a 3rd embodiment. It is a SEM image of the carbon material produced by the manufacturing method different from a 3rd embodiment. It is a flowchart which shows the manufacturing method of the bacteria-produced cellulose carbon which concerns on 4th Embodiment of this invention. It is a SEM image of the skin part of the carbon material obtained by example 1 of an experiment. It is a SEM image of the section of the carbon material obtained by example 1 of an experiment. It is a SEM image of the carbon material obtained by example 2 of an experiment. It is a SEM image of the carbon material obtained by comparative example 1. It is a SEM image of the carbon material obtained by comparative example 2.

Hereinafter, embodiments of the present invention will be described using the drawings.

First Embodiment
FIG. 1 is a flowchart showing a method of producing cellulose nanofiber carbon according to the first embodiment of the present invention. In the following description, cellulose nanofiber carbon may be referred to as a carbon material.

The method for producing cellulose nanofiber carbon of the present embodiment includes a dispersion step (step S1), a freezing step (step S2), a drying step (step S3), and a carbonization step (step S4). In this production method, a cellulose nanofiber solution is required.

The form of the cellulose nanofibers in the cellulose nanofiber solution is preferably a dispersed form. Therefore, although the dispersion process (step S1) is included in the manufacturing process shown in FIG. 1, the dispersion process (step S1) may be omitted. That is, when using the solution of the form which the cellulose nanofiber disperse | distributed, the said process is unnecessary.

The dispersing step disperses the cellulose nanofibers contained in the cellulose nanofiber solution. The dispersion medium is an aqueous system such as water (H 2 O) or a carboxylic acid, methanol (CH 3 OH), ethanol (C 2 H 5 OH), propanol (C 3 H 7 OH), n-butanol, isobutanol, n-butylamine, dodecane, unsaturated fatty acid, ethylene Organic systems such as glycol, heptane, hexadecane, isoamyl alcohol, octanol, isopropanol, acetone, and glycerin, and two or more of them may be mixed.

Dispersion of the cellulose nanofibers may be performed using, for example, a homogenizer, an ultrasonic cleaner, an ultrasonic homogenizer, a magnetic stirrer, a stirrer, a shaker, or the like.

The solid content concentration of the cellulose nanofibers in the cellulose nanofiber solution is preferably 0.001 to 80% by mass, and more preferably 0.01 to 30% by mass.

A freezing process freezes the solution containing a cellulose nanofiber, and obtains a frozen body (step S2). In this step, for example, the cellulose nanofiber solution contained in a test tube is contained in a suitable container such as a test tube and cooled around the test tube in a coolant such as liquid nitrogen. It does by freezing.

The method of freezing is not particularly limited as long as the dispersion medium of the solution can be cooled below the freezing point, and may be cooled by a freezer or the like. By freezing the cellulose nanofiber solution, the dispersion medium loses its fluidity, the dispersoid cellulose nanofibers are fixed, and a three-dimensional network structure is constructed.

In the drying step, the frozen body frozen in the freezing step is dried in vacuum to obtain a dried body (step S3). This process sublimes the frozen dispersion medium from the solid state. For example, the obtained frozen body is stored in a suitable container such as a flask, and the inside of the container is evacuated. By disposing the frozen body under a vacuum atmosphere, the sublimation point of the dispersion medium is lowered, and it is possible to sublimate even a substance that does not sublime at normal pressure.

The degree of vacuum in the drying step varies depending on the dispersion medium to be used, but is not particularly limited as long as the dispersion medium is a degree of vacuum which is sublimed. For example, when water is used as the dispersion medium, it is necessary to set the pressure to a degree of vacuum of 0.06 MPa or less, but since heat is taken away as the latent heat of sublimation, it takes time to dry. Therefore, the degree of vacuum is preferably 1.0 × 10 −6 Pa to 1.0 × 10 −2 Pa. Furthermore, heat may be applied using a heater or the like at the time of drying.

In the carbonization step, the dried product dried in the drying step is carbonized by heating in a non-burning atmosphere to obtain cellulose nanofiber carbon (step S4). The carbonization of cellulose nanofibers may be carried out by firing at 200 ° C. to 2000 ° C., more preferably 600 ° C. to 1800 ° C. in an inert gas atmosphere for carbonization. As a gas which does not burn cellulose, inert gas, such as nitrogen gas and argon gas, may be sufficient, for example. Further, the gas which does not burn cellulose may be a reducing gas such as hydrogen gas or carbon monoxide gas, or may be carbon dioxide gas. More preferable is carbon dioxide gas or carbon monoxide gas which has an activating effect on carbon materials and can be expected to be highly activated.

According to the method for producing cellulose nanofiber carbon described above, the cellulose nanofibers as the dispersoid are fixed by the freezing step to construct a three-dimensional network structure. In addition, the drying process can take out the cellulose nanofibers while maintaining the three-dimensional network structure. Therefore, a sufficient specific surface area can be obtained, and the production of a high specific surface area carbon material is facilitated.

2A and 2B are SEM (Scanning Electron Microscope) images of cellulose nanofiber carbon. The magnification is 10000 times.

FIG. 2A is a SEM image of cellulose nanofiber carbon produced by the production method of the present embodiment. The image shows that the cellulose nanofibers are fixed and a three-dimensional network structure is constructed.

FIG. 2B shows the appearance of cellulose nanofiber carbon when it is dried in the air and carbonized unlike the manufacturing method of the present embodiment. Since the frozen body changes from solid to liquid and liquid to gas, the three-dimensional network structure of cellulose nanofibers is destroyed. As shown in FIG. 2B, when the three-dimensional network structure is destroyed, it is difficult to make a high specific surface area carbon material.

As described above, the cellulose nanofiber carbon produced by the production method of the present embodiment is a stretchable carbon material having a three-dimensional network structure of co-continuum in which cellulose nanofibers are connected. In addition, the cellulose nanofiber carbon of the present embodiment has high conductivity, corrosion resistance, and high specific surface area.

Therefore, the cellulose nanofiber carbon produced by the production method of the present embodiment is a battery, a capacitor, a fuel cell, a biofuel cell, a microbial cell, a catalyst, a solar cell, a semiconductor production process, a medical device, a beauty tool, a filter, It is suitable as a heat resistant material, a flame resistant material, a heat insulating material, a conductive material, an electromagnetic wave shielding material, an electromagnetic wave noise absorbing material, a heating element, a microwave heating element, a cone paper, clothes, carpet, mirror fog prevention, a sensor, a touch panel and the like.

Second Embodiment
FIG. 3 is a flowchart showing a method of producing cellulose nanofiber carbon according to the second embodiment. The manufacturing method shown in FIG. 3 includes a crushing step (step S5), a mixing step (step S6), and a drying step (step S7), as compared with the manufacturing method of the first embodiment.

In the pulverizing step, the dried product (cellulose nanofiber carbon) carbonized in the above-mentioned carbonizing step (step S4) is pulverized (step S5). The grinding process may be carried out using, for example, a mixer, homogenizer, ultrasonic homogenizer, high-speed rotational shear stirrer, colloid mill, roll mill, high-pressure jet disperser, rotary ball mill, vibration ball mill, planetary ball mill, attritor, etc. The nanofiber carbon is powdered or slurried.

In this case, the cellulose nanofiber carbon preferably has a secondary particle diameter of 10 nm to 20 mm, and more preferably 50 nm to 1 mm. This is because when the secondary particle diameter is reduced to 10 nm or less, the co-continuous structure by the cellulose nanofibers is broken, it becomes difficult to obtain sufficient binding strength and conductive path, and the electrical resistance is increased. In order to In addition, when the secondary particle diameter is 20 mm or more, the cellulose nanofibers functioning as a binder are not sufficiently dispersed, and it becomes difficult to maintain in the form of a sheet.

In addition, since cellulose nanofiber carbon has a high porosity and a low density, when cellulose nanofiber carbon is pulverized alone, cellulose nanofiber carbon powder scatters during or after pulverization, making it difficult to handle. Therefore, it is preferable to impregnate cellulose nanofiber carbon with a solvent and then to grind it. The solvent used here is not particularly limited, but, for example, an aqueous system such as water (H 2 O) or a carboxylic acid, methanol (CH 3 OH), ethanol (C 2 H 5 OH), propanol (C 3 H 7 OH), n-butanol, isobutanol, n- Organic systems such as butylamine, dodecane, unsaturated fatty acid, ethylene glycol, heptane, hexadecane, isoamyl alcohol, octanol, isopropanol, acetone, glycerin and the like, and two or more of these may be mixed.

In the mixing step, the material pulverized in the grinding step (step S5) and the cellulose nanofiber solution dispersed in the dispersing step (step S1) are mixed to obtain a mixed solution (step S6). The mixed solution is in the form of slurry, and by drying the mixed slurry, it is possible to process cellulose nanofiber carbon into a sheet.

A drying process removes a liquid from a liquid mixture (Step S7). When the slurry-like mixed liquid (mixed slurry) is dried, a constant temperature bath, a vacuum dryer, an infrared dryer, a hot air dryer, a suction dryer, or the like may be used. Furthermore, it can be rapidly dried by suction filtration using an aspirator or the like.

After the mixed slurry obtained by the manufacturing method of the present embodiment described above is dried and made into a sheet, it may be processed into a desired shape. The sheet-like carbon material can be processed into a desired shape by applying the mixed slurry to an arbitrary shape and then drying it. By applying it in an arbitrary shape, it is possible to reduce the cost of materials such as scraps generated in the cutting process, and it is possible to obtain a carbon material of any shape according to the preference of the user. Also, the strength of the carbon material can be enhanced.

Note that the manufacturing method of the present embodiment may not include all the steps. For example, cellulose nanofiber carbon in a crushed state may be used up to the grinding step. To use is to distribute in that state. Similarly, the process may be carried out up to the mixing step and circulated in the state of the mixed slurry.

In order to confirm the effects of the manufacturing method of the first embodiment and the second embodiment described above, a carbon material (Experimental Example 1-3) manufactured by the manufacturing method of the first embodiment and the second embodiment, and the carbon material An experiment was conducted to compare with carbon materials (Comparative Examples 1 and 2) manufactured by a manufacturing method different from that of the embodiment.

(Experimental example 1)
Using a cellulose nanofiber (manufactured by Nippon Paper Industries Co., Ltd.), 1 g of cellulose nanofiber and 10 g of ultrapure water are stirred with a homogenizer (manufactured by SMT) for 12 hours to prepare a dispersion of cellulose nanofiber, and the test tube is prepared. I poured it.

The cellulose nanofiber solution was completely frozen by immersing the test tube in liquid nitrogen for 30 minutes. After completely freezing the cellulose nanofiber solution, the frozen cellulose nanofiber solution is taken out on a petri dish, and dried by a freeze dryer (manufactured by Tokyo Scientific Instruments Co., Ltd.) under a vacuum of 10 Pa or less. A dried cellulose nanofiber was obtained. After drying in vacuum, the cellulose nanofibers were carbonized by firing at 600 ° C. for 2 hours under a nitrogen atmosphere, whereby a carbon material of Experimental Example 1 was produced.

(Experimental example 2)
After impregnating the carbon material produced in Experimental example 1 with water, stirring the carbon material and the cellulose nanofiber solution (carbon material: cellulose nanofiber solution weight ratio 1: 1) with a homogenizer (made by SMT) for 12 hours Then, it was crushed and mixed. This mixture was in the form of a slurry, and was subjected to suction filtration using an aspirator (manufactured by Shibata Scientific Co., Ltd.) to separate the carbon material from the filter paper. Thereafter, the carbon material was placed in a thermostatic bath, and was subjected to drying treatment at 60 ° C. for 12 hours to produce a carbon material of Experimental Example 2.

(Experimental example 3)
The skin portion of the carbon material produced in Experimental Example 1 was stripped of only the skin portion using a cutter or the like to produce a carbon material of Experimental Example 3. That is, the surface of the carbon material produced in Experimental Example 1 was removed, and the carbon material of Experimental Example 3 was produced.

(Comparative example 1)
Comparative Example 1 is a carbon material produced by ordinary drying without performing the above-described freezing step and drying step.

In Comparative Example 1, the cellulose nanofiber solution prepared in Experimental Example 1 was poured into a petri dish, placed in a thermostat, and subjected to drying treatment at 60 ° C. for 12 hours. Thereafter, the cellulose nanofibers were carbonized by baking for 2 hours at 600 ° C. in a nitrogen atmosphere, whereby a carbon material was produced.

(Comparative example 2)
After impregnating the carbon material produced in Comparative Example 1 (usually drying) with water, the carbon material and cellulose nanofiber solution (weight ratio of carbon material: cellulose nanofiber solution 1: 1) of 12 with a homogenizer (made by SMT) are used. Grinding and mixing were performed by stirring for a period of time. This mixture was in the form of a slurry, and was subjected to suction filtration using an aspirator (manufactured by Shibata Scientific Co., Ltd.) to separate the carbon material from the filter paper. Thereafter, the carbon material was put in a thermostatic bath, and the drying process was performed at 60 ° C. for 12 hours to prepare a carbon material of Comparative Example 2.

(Evaluation method)
The obtained carbon material was evaluated by performing XRD measurement, SEM observation, porosity measurement, tensile test, and BET specific surface area measurement. This carbon material was confirmed to be carbon (C, PDF card No. 01-071-4630) single phase by XRD measurement. The PDF card No. is a card number of PDF (Powder Diffraction File) which is a database collected by the International Center for Diffraction Data (ICDD).

SEM images of the produced carbon material are shown in FIGS. 4A to 4E. Moreover, the evaluation value obtained by measuring is shown in Table 1.

FIGS. 4A to 4E are SEM images of the carbon materials obtained in Experimental Examples 1 and 2 and Comparative Examples 1 and 2. FIG. 4A is a SEM image of the skin portion (surface) of the carbon material obtained in Experimental Example 1. As shown to FIG. 4A, the skin part of the carbon material of Experimental example 1 has some aggregation seen. FIG. 4B is a SEM image of a cross section cut to remove the skin of the carbon material of FIG. 4A. FIG. 4C is a SEM image of the surface of the carbon material obtained in Experimental Example 2. FIG. 4D is a SEM image of the surface of the carbon material obtained in Comparative Example 1. FIG. 4E is a SEM image of the surface of the carbon material obtained in Comparative Example 2. In each case, the magnification is 10,000 times.

As shown in FIGS. 4B and 4C (Experimental Examples 1 and 2), in the carbon material obtained by the manufacturing method of the first embodiment and the second embodiment, nanofibers with a fiber diameter of several tens of nm are continuously connected. It can be confirmed that it is a co-continuous body.

On the other hand, as shown in FIG. 4D and FIG. 4E (comparative examples 1 and 2), it can be confirmed that the carbon material in which the cellulose nanofiber solution is usually dried is a carbon material which has no pores and is densely aggregated.

As shown in Table 1, the carbon materials (Experimental Examples 1 and 2) of the first embodiment and the second embodiment have surface tensions of water accompanying evaporation of the dispersion medium than Comparative Examples 1 and 2 in which drying is normally performed. It is possible to suppress cohesion due to As a result, it has been confirmed that it is possible to provide a carbon material having high specific surface area and high porosity and excellent performance.

Moreover, Experimental example 3 is a carbon material produced by peeling the skin part (FIG. 4A) of the carbon material manufactured by Experimental example 1. FIG. The SEM image of this experimental example 3 is the same as that of FIG. 4B. Therefore, the carbon material of Experimental Example 3 has excellent performance with a high specific surface area and a high porosity. As shown in FIG. 4A, it is considered that a part of the skin of the carbon material obtained by the manufacturing method of Experimental Example 1 is agglutinated and that the aggregates of the skin are removed.

As shown in Table 1, in Experimental Example 1, it could be confirmed that the film had excellent stretchability even after carbonization. Moreover, in Experimental example 2, it has confirmed that it had the outstanding tensile strength.

Thus, the step of freezing the solution containing cellulose nanofibers to obtain a frozen body, the step of drying the frozen body in a vacuum to obtain a dried body, and heating in an atmosphere of gas in which the dried body does not burn Since the production method of the present embodiment including the carbonization step of carbonization is carbonized by heat-treating cellulose nanofibers, excellent specific surface area, strength, and porosity can be obtained.

The carbon material manufactured by the manufacturing method of the first embodiment and the second embodiment can use cellulose derived from a natural product, and has very low environmental impact. Such carbon materials can be easily disposed of in daily life, so small devices, sensor terminals, medical devices, batteries, beauty instruments, fuel cells, biofuel cells, microbial cells, capacitors, catalysts, Solar cell, semiconductor manufacturing process, filter, heat resistant material, flame resistant material, heat insulating material, conductive material, electromagnetic wave shielding material, electromagnetic wave noise absorbing material, heating element, microwave heating element, cone paper, clothes, carpet, mirror fog prevention, sensor It can be effectively used in various situations including the touch panel and the like.

Third Embodiment
In the third embodiment and the fourth embodiment described later, a gel containing cellulose nanofibers is used instead of the solution containing the cellulose nanofibers of the first embodiment. Moreover, the gel of the third embodiment and the fourth embodiment is a bacteria-produced gel in which cellulose nanofibers are dispersed using bacteria. Therefore, the cellulose nanofiber carbon manufactured by the manufacturing method of 3rd Embodiment and 4th Embodiment is called bacterial production cellulose carbon in subsequent description.

FIG. 5 is a flowchart showing a method of producing bacterial cellulose carbon produced according to a third embodiment of the present invention. In the following description, bacterial cellulose carbon may be referred to as a carbon material.

The method for producing the bacteria-produced cellulose carbon according to the present embodiment includes a gel production step (step S11), a freezing step (step S12), a drying step (step S13), and a carbonization step (step S14).

In the gel forming step, bacteria are used to form a bacteria-produced gel in which cellulose nanofibers are dispersed (Step S11). Here, gel means that the dispersion medium loses fluidity and becomes solid due to the three-dimensional network structure of the nanostructure which is a dispersoid. Specifically, it means a dispersion having a shear modulus of 102 to 106 Pa. The dispersion medium of the gel may be an aqueous system such as water (H 2 O) or a carboxylic acid, methanol (CH 3 OH), ethanol (C 2 H 5 OH), propanol (C 3 H 7 OH), n-butanol, isobutanol, n-butylamine, dodecane, unsaturated fatty acid And organic systems such as ethylene glycol, heptane, hexadecane, isoamyl alcohol, octanol, isopropanol, acetone, and glycerin, and two or more of them may be mixed.

The gel produced by the bacteria has a nano-sized nanofiber as a basic structure, and by using this gel to produce a carbon material, the resulting carbon material has a high specific surface area. Specifically, synthesis of a carbon material having a specific surface area of 300 m 2 / g or more is possible by using a gel produced by bacteria.

The bacteria-produced gel has a structure in which the nanofibers are entangled in a coil or network, and further has a branched structure based on bacterial growth, so that the carbon material produced has an elastic limit. Achieves excellent stretchability with 50% or more of distortion.

Examples of the bacteria include known ones, for example, Acetobacter xylinum subspecies schlofermenta, Acetobacter xylinum ATCC 23768, Acetobacter xylinum ATCC 23769, Acetobacter pastilian ATCC 10245, Acetobacter xylinum ATCC 14851, acetobacter It may be produced by culturing acetic acid bacteria such as Bacter xylinum ATCC 11142 and Acetobacter xylinum ATCC 10821. Also, the bacteria may be produced by culturing various mutant strains created by mutating these acetic acid bacteria by a known method using NTG (nitrosoguanidine) or the like.

In the freezing step, the bacterial gel is frozen to obtain a frozen body (step S12). In the freezing step, for example, the bacteria-producing gel is stored in a suitable container such as a test tube, and the periphery of the test tube is cooled in a coolant such as liquid nitrogen to freeze the bacteria-producing gel contained in the test tube. It is carried out by doing. The method of freezing is not particularly limited as long as the dispersion medium of the gel can be cooled below the freezing point, and may be cooled by a freezer or the like.

By freezing the bacteria-produced gel, the dispersion medium loses its fluidity, the dispersoid cellulose nanofibers are immobilized, and a three-dimensional network structure is constructed.

In the drying step, the frozen body is dried in vacuum to obtain a dried body (bacteria-produced xerogel) (step S13). In the drying step, the frozen body obtained in the freezing step is dried in vacuum, and the frozen dispersion medium is sublimed from the solid state. For example, the obtained frozen body is stored in a suitable container such as a flask, and the inside of the container is evacuated. By disposing the frozen body under a vacuum atmosphere, the sublimation point of the dispersion medium is lowered, and it is possible to sublimate even a substance that does not sublime at normal pressure.

The degree of vacuum in the drying step varies depending on the dispersion medium to be used, but is not particularly limited as long as the dispersion medium is a degree of vacuum which is sublimed. For example, when water is used as the dispersion medium, it is necessary to set the pressure to a degree of vacuum of 0.06 MPa or less, but since heat is taken away as the latent heat of sublimation, it takes time to dry. Therefore, the degree of vacuum is preferably 1.0 × 10 −6 to 1.0 × 10 −2 Pa. Furthermore, heat may be applied using a heater or the like during drying.

In the carbonization step, the dried product (bacteria-produced xerogel) is carbonized by heating in an atmosphere that does not burn it, and bacterial-produced cellulose carbon is obtained (Step S14). The carbonization of the bacterially produced xerogel may be carried out by firing at 500 ° C. to 2000 ° C., more preferably 900 ° C. to 1800 ° C. in an inert gas atmosphere. As a gas which does not burn cellulose, inert gas, such as nitrogen gas and argon gas, may be sufficient, for example. Further, the gas which does not burn cellulose may be a reducing gas such as hydrogen gas or carbon monoxide gas, or may be carbon dioxide gas. In the present embodiment, it is more preferable to use carbon dioxide gas or carbon monoxide gas which has an activation effect on carbon materials and can be expected to be highly activated.

According to the method for producing bacterial cellulose carbon produced as described above, the cellulose nanofibers as the dispersoid are fixed by the freezing step to construct a three-dimensional network structure. In addition, the drying process can take out the cellulose nanofibers while maintaining the three-dimensional network structure. Therefore, a sufficient specific surface area can be obtained, and the production of a high specific surface area carbon material is facilitated.

6A and 6B are SEM images of cellulose nanofiber carbon. The magnification is 10000 times.

FIG. 6A is a SEM image of bacterial cellulose carbon produced by the manufacturing method of the present embodiment. The image shows that the cellulose nanofibers are fixed and a three-dimensional network structure is constructed.

FIG. 6B shows the appearance of the carbon material when it is dried in the air and carbonized unlike the manufacturing method of the present embodiment. Since the frozen body changes from solid to liquid and liquid to gas, the three-dimensional network structure of cellulose nanofibers is destroyed. As shown in FIG. 6B, when the three-dimensional network structure is destroyed, it is difficult to produce a high specific surface area carbon material.

As described above, the bacteria-produced cellulose carbon produced by the production method of the present embodiment is a carbon material having a three-dimensional network structure and having stretchability. The bacterial cellulose carbon of the present embodiment has high conductivity, corrosion resistance, and high specific surface area.

Therefore, the bacteria-produced cellulose carbon produced by the production method of the present embodiment can enhance the adhesion to electrodes, voids, living tissues, device connection parts and the like. The bacterially produced cellulose carbon of the present embodiment has high conductivity, corrosion resistance, and high specific surface area, and therefore, cells, capacitors, fuel cells, biofuel cells, microbial cells, catalysts, solar cells, semiconductor manufacturing processes , Medical equipment, beauty instruments, filters, heat resistant materials, flame resistant materials, heat insulating materials, conductive materials, electromagnetic wave shielding materials, electromagnetic wave noise absorbing materials, heating elements, microwave heating elements, cone paper, clothes, carpets, mirror fog prevention, Suitable for sensors, touch panels, etc.

Fourth Embodiment
FIG. 7 is a flowchart showing a method of producing bacterial cellulose carbon produced according to the fourth embodiment. The manufacturing method shown in FIG. 7 is different from the manufacturing method of the third embodiment in the first crushing step (step S15), the second crushing step (step S16), the mixing step (step S17), and the applying step (step S18). And a drying step (step S19).

A 1st grinding process grinds the dried body (bacterial-producing cellulose carbon) carbonized by said carbonization process (step S14) (step S15). The first crushing step uses, for example, a mixer, a homogenizer, an ultrasonic homogenizer, a high-speed rotational shear stirrer, a colloid mill, a roll mill, a high pressure jet disperser, a rotary ball mill, a vibrating ball mill, a planetary ball mill, an attritor, etc. , Make bacterially produced cellulose carbon powder or slurry. In this case, the bacterial particle-produced cellulose carbon preferably has a secondary particle diameter of 100 nm to 5 mm, and more preferably 1 μm to 1 mm. This is because when the secondary particle diameter is reduced to 100 nm or less, the co-continuous structure by cellulose nanofibers is broken, it becomes difficult to obtain sufficient binding strength and conductive path, and the electrical resistance is increased. In order to In addition, when the secondary particle diameter is 5 mm or more, the bacteria-produced gel that functions as a binding agent is not sufficiently dispersed, and it becomes difficult to maintain the sheet shape.

Further, bacterially produced cellulose carbon has a high porosity and a low density, and therefore, when the carbon material is crushed alone, powder of bacterially produced cellulose carbon is scattered during or after the pulverization and handling is difficult. Therefore, it is preferable to impregnate the bacteria-produced cellulose carbon with a solvent and then to grind it. The solvent used here is not particularly limited, but, for example, an aqueous system such as water (H 2 O) or a carboxylic acid, methanol (CH 3 OH), ethanol (C 2 H 5 OH), propanol (C 3 H 7 OH), n-butanol, isobutanol, n- Organic systems such as butylamine, dodecane, unsaturated fatty acid, ethylene glycol, heptane, hexadecane, isoamyl alcohol, octanol, isopropanol, acetone, glycerin and the like, and two or more of these may be mixed.

In the second crushing step, the bacterial gel produced in the gel formation step is crushed (step S16). In addition, it is also possible to grind | pulverize bacterial production gel and bacterial production cellulose carbon simultaneously. In that case, the mixing step can be omitted.

In the mixing step, the materials ground in each of the first grinding step and the second grinding step are mixed (step S17). The mixture is in the form of a slurry.

In the coating process, the slurry-like mixture is formed into an arbitrary shape (step S18).

In the drying step, the liquid is removed from the mixture formed (coated) in an arbitrary shape in the coating step (step S19). When the slurry mixture (mixed slurry) is dried, a constant temperature bath, a vacuum dryer, an infrared dryer, a hot air dryer, a suction dryer, or the like may be used. Furthermore, it can be rapidly dried by suction filtration using an aspirator or the like.

The mixed slurry obtained by the manufacturing method of the present embodiment described above may be dried without performing the application step to form a sheet, and then processed into a desired shape. After the mixed slurry is formed into an arbitrary shape, the sheet-like carbon material can be processed into a desired shape by drying. In addition, by applying in the application step, the material cost such as scraps produced in the cutting process can be reduced, and it is possible to obtain a carbon material having an arbitrary shape according to the preference of the user. Also, the strength of the carbon material can be enhanced.

Note that the manufacturing method of the present embodiment may not include all the steps. For example, bacteria-produced cellulose carbon in a crushed state may be used up to the first crushing step. To use is to distribute in that state. Similarly, the process may be carried out up to the mixing step and circulated in the state of the mixed slurry.

In order to confirm the effects of the manufacturing method of the third embodiment and the fourth embodiment described above, a carbon material (Experimental Example 1-3) manufactured by the manufacturing method of the third embodiment and the fourth embodiment, An experiment was conducted to compare with carbon materials (Comparative Examples 1 and 2) manufactured by a manufacturing method different from that of the embodiment.

(Experimental example 1)
Use natadecoco (Fujicco) as a bacterial cellulose gel produced by the acetobacterium Acetobacter xylinum and completely freeze the bacteria-produced gel by soaking in liquid nitrogen for 30 minutes in a foam polystyrene box. The After completely freezing the bacteria-produced gel, the frozen bacteria-produced gel is taken out on a petri dish, and dried by a freeze dryer (manufactured by Tokyo Scientific Instruments Co., Ltd.) under a vacuum of 10 Pa or less to produce bacteria. I got a xerogel. After drying the bacteria-produced xerogel in vacuo, the bacteria-produced xerogel was carbonized by baking for 2 hours at 600 ° C. under a nitrogen atmosphere, whereby a carbon material of Experimental Example 1 was produced.

(Experimental example 2)
After impregnating the carbon material prepared in Experimental Example 1 with water, the carbon material and bacterial gel (carbon material: bacterial gel weight ratio 1: 1) are stirred for 12 hours with a homogenizer (manufactured by SMT). It was crushed and mixed. This mixture was in the form of a slurry, and was subjected to suction filtration using an aspirator (manufactured by Shibata Scientific Co., Ltd.) to separate the carbon material from the filter paper. Thereafter, the carbon material was placed in a thermostatic bath, and was subjected to drying treatment at 60 ° C. for 12 hours to produce a carbon material of Experimental Example 2.

(Experimental example 3)
The skin portion of the carbon material produced in Experimental Example 1 was stripped of only the skin portion using a cutter to produce a carbon material of Experimental Example 3.

In Comparative Example 1, the bacteria-produced gel used in Experimental Example 1 was placed in a thermostat and subjected to drying treatment at 60 ° C. for 12 hours. Thereafter, the bacteria-produced cellulose was carbonized by baking for 2 hours at 600 ° C. in a nitrogen atmosphere, whereby a carbon material was produced.

(Comparative example 2)
The carbon material prepared in Comparative Example 1 (normally dried) was impregnated with water, and then stirred for 12 hours with homoenergy (manufactured by S.M.T.), and pulverized to prepare a slurry in which the carbon material was dispersed. Then, the slurry and the bacterial gel (carbon material: bacterial gel weight ratio 1: 1) were stirred for 12 hours to perform grinding and mixing.

Thereafter, suction filtration was performed using an aspirator (manufactured by Shibata Scientific Co., Ltd.) to peel the carbon material from the filter paper. Then, the carbon material was put into a thermostat, and the drying process was performed at 60 degreeC for 12 hours, and the carbon material of the comparative example 2 was produced.

SEM images of the produced carbon material are shown in FIGS. 8A to 8E. Moreover, the evaluation value obtained by measuring is shown in Table 2.

FIGS. 8A to 8E are SEM images of the carbon materials obtained in Experimental Examples 1 and 2 and Comparative Examples 1 and 2. FIG. FIG. 8A is a SEM image of the skin portion (surface) of the carbon material obtained in Experimental Example 1. As shown in FIG. 8A, in the skin portion of the carbon material of Experimental Example 1, partial aggregation is observed. FIG. 8B is a SEM image of a cross section cut to remove the skin of the carbon material of FIG. 8A. FIG. 8C is a SEM image of the surface of the carbon material obtained in Experimental Example 2. FIG. 8D is a SEM image of the surface of the carbon material obtained in Comparative Example 1. FIG. 8E is a SEM image of the surface of the carbon material obtained in Comparative Example 2. In each case, the magnification is 10,000 times.

As shown in FIGS. 8B and 8C (Experimental Examples 1 and 2), in the carbon materials obtained by the manufacturing methods of the third and fourth embodiments, nanofibers with a fiber diameter of several tens of nm are continuously connected. It can be confirmed that it is a co-continuous body.

On the other hand, as shown in FIG. 8D and FIG. 8E (comparative examples 1 and 2), the carbon material obtained by usually drying the bacteria-producing gel containing water is a carbon material which has no pores and is densely aggregated. Can be confirmed.

As shown in Table 2, the carbon materials (Experimental Examples 1 and 2) of the third embodiment and the fourth embodiment are associated with the evaporation of the dispersion medium than the drying process of Comparative Examples 1 and 2 in which the drying is usually performed. It is possible to suppress aggregation due to surface tension of the As a result, it has been confirmed that it is possible to provide a carbon material having high specific surface area and high porosity and excellent performance.

Moreover, Experimental example 3 is a carbon material produced by peeling the skin part (FIG. 4A) of the carbon material manufactured by Experimental example 1. FIG. The SEM image of this experimental example 3 is the same as that of FIG. 8B. Therefore, the carbon material of Experimental Example 3 has excellent performance with a high specific surface area and a high porosity. As shown in FIG. 8A, this is considered to be that the skin portion of the carbon material obtained by the manufacturing method of Experimental Example 1 is partially aggregated, and the aggregates of the skin portion are removed.

As shown in Table 2, in Experimental Example 1, it could be confirmed that the film had excellent stretchability even after carbonization. Moreover, in Experimental example 2, it has confirmed that it had the outstanding tensile strength.

Thus, the manufacturing method of the third embodiment and the fourth embodiment comprises the steps of freezing the gel produced by bacteria to obtain a frozen body, and drying the frozen body in a vacuum to obtain a dried body. And a carbonization step of heating and carbonizing the dried body in an atmosphere of non-combustible gas. Since the bacterially produced cellulose is carbonized by heat treatment, the bacterially produced cellulose carbon produced in the third and fourth embodiments can achieve excellent specific surface area, strength, and porosity.

The carbon material manufactured by the manufacturing method of the third embodiment and the fourth embodiment can also use cellulose derived from a natural product, and has very low environmental impact. Such carbon materials can be easily disposed of in daily life, so small devices, sensor terminals, medical devices, batteries, beauty instruments, fuel cells, biofuel cells, microbial cells, capacitors, catalysts, Solar cell, semiconductor manufacturing process, filter, heat resistant material, flame resistant material, heat insulating material, conductive material, electromagnetic wave shielding material, electromagnetic wave noise absorbing material, heating element, microwave heating element, cone paper, clothes, carpet, mirror fog prevention, sensor It can be effectively used in various situations including the touch panel and the like.

In addition, this invention is not limited to said embodiment, A deformation | transformation is possible within the range of the summary.

For example, as described in Example 3 of Table 1 and Table 3, after the carbonization step (see FIGS. 1 and 5) of the first and third embodiments, the surface of the carbon material produced in the carbonization step You may perform the removal process which peels only a skin part using a cutter etc. for the part.

Similarly, after the carbonization step (refer to FIG. 3 and FIG. 7) of the second embodiment and the fourth embodiment, the skin portion of the carbon material produced in the carbonization step is peeled away using a cutter or the like to peel only the skin portion. A step may be performed and then the subsequent steps may be performed.

S1: dispersing step S2: freezing step S3: drying step S4: carbonization step S5: grinding step S6: drying step

Claims

A method for producing cellulose nanofiber carbon, which carbonizes cellulose nanofiber, comprising:
Freezing the solution or gel containing the cellulose nanofibers to obtain a frozen body;
Drying the frozen body in vacuum to obtain a dried body;
And D. a carbonizing step of heating and carbonizing the dried product in an atmosphere that does not burn the cellulose to obtain a cellulose nanofiber carbon.
In the method for producing cellulose nanofiber carbon according to claim 1,
A manufacturing method of cellulose nanofiber carbon characterized by including: a grinding process which grinds said dry object carbonized at said carbonization process.
In the method for producing cellulose nanofiber carbon according to claim 2,
A method for producing cellulose nanofiber carbon, comprising: a mixing step of mixing a material pulverized in the pulverizing step with a cellulose nanofiber solution to obtain a mixed solution.
In the method for producing cellulose nanofiber carbon according to claim 3,
A method for producing cellulose nanofiber carbon, comprising: a drying step of removing a liquid from the mixed solution.
In the method for producing cellulose nanofiber carbon according to claim 1,
A method for producing cellulose nanofiber carbon, comprising a gel forming step of dispersing the cellulose nanofibers using bacteria to form the gel.
In the method for producing cellulose nanofiber carbon according to claim 5,
A method of producing cellulose nanofiber carbon, comprising: a first pulverizing step of pulverizing the dried body carbonized in the carbonizing step.
In the method for producing cellulose nanofiber carbon according to claim 6,
A second pulverizing step of pulverizing the bacteria-produced cellulose produced in the gel forming step;
A method for producing cellulose nanofiber carbon, comprising: a mixing step of mixing the materials crushed in each of the first grinding step and the second grinding step.
In the method for producing cellulose nanofiber carbon according to claim 7,
Applying the mixture mixed in the mixing step to form an arbitrary shape;
And d) removing the liquid from the mixture.
Cellulose nanofiber carbon characterized by having a three-dimensional network structure of co-continuum in which cellulose nanofibers are connected.
Cellulose nanofiber carbon characterized by having a three-dimensional network structure which is a continuum in which nanofibers of bacterial gel are connected.